"Let us not grow weary in doing what is right, for we will reap at harvest time, if we do not give up"-Galatians 6:9 (NRSV).  

The Bible tells us our justification isn't by doing what is right, but by faith in Christ (Romans 3:28).  But, James, in 2:18, says he will show you his faith by doing what is right.  Faith and works go hand in hand...or as Forrest Gump would say...like peas and carrots.  The only way to keep from growing weary, in doing what is right and in faith, is to exercise...spiritually and physically.  Daily Bible reading and prayer strengthen you spiritually and being active builds your physical stamina.  Don't give up!  Think like Forrest...spiritual and physical exercise go together...like peas and carrots...building a muscular temple and a muscular faith.  Then you will be well prepared for the reaping.